I wonder if, other than in the odd case such as that of your mother, with her Argentine influence, the term was ever commonly used in English to mean "child" in a generic sense? Or did the term enter English in a context in which it was automatically applied to black children; e.g., in some branch of the slave trade? I've never before heard of the term being applied to white children; if it was at one time not uncommon in England/Ireland/Scotland - etc. - I wonder if it was picked up from Southern-American-related culture (e.g., from Uncle Tom's Cabin) as a kind of endearment?